This invention relates to the enhancement of surface heat transfer for either heating or cooling in a variety of devices including gas turbine airfoils, combustion liners, transition pieces and the like. Specifically, the invention relates to unique linear surface concavities wherein each individual cavity overlaps an adjacent cavity by a discrete amount.
Enhancement of surface heat transfer for cooling (or heating) is required to improve thermal performance for a variety of devices, including gas turbine airfoils, combustor liners, transition pieces, or other heat transfer devices including plate fins on motors, generators, etc. Cooling mechanisms that provide high thermal enhancement factors with low enhancement of friction coefficients are sought for these applications.
Many surface treatments have been devised and used to address this problem. One very common method is the use of discrete turbulators, also known as xe2x80x9ctrip stripsxe2x80x9d or xe2x80x9crib rougheners,xe2x80x9d designed to disrupt the flow and thereby enhance heat transfer on the surface to be cooled. This method has very high pressure losses, however. Another common method is the use of arrays of pin fins or pedestals that protrude from a component wall into the flow. These act in similar fashion to turbulators, but are generally used in regions of more restricted geometry. A third method is the use of arrays of discrete surface concavities or dimples, which enhance heat transfer through the formation of flow vortices while maintaining a lower pressure loss compared to other methods. An example of the use of surface concavities on the cold side of a combustor liner is disclosed in U.S. Pat. No 6,098,397.
The present invention provides a unique geometry for a linear arrangement of concavities of various shapes, in which each concavity overlaps the adjacent concavity by a discrete amount. Arranged in a continuous line, this configuration may be referred to as a xe2x80x9clinear surface concavityxe2x80x9d and, in some circumstances, has distinct advantages over conventional cavity arrays.
By overlapping adjacent concavities, a continuous xe2x80x9cchannelxe2x80x9d feature is provided with a continuous enhancement, i.e., there are no gaps between the concavities. It is crucial that the concavities overlap to provide this continuous enhancement mechanism, otherwise they will simply act as individual cooling enhancements. For example, turbulators have separated flow zones requiring certain minimum flow reattachment lengths between adjacent turbulators. This xe2x80x9clinear surface concavityxe2x80x9d design is also distinct from a constant cross section trench or channel, where there is no organized vortex formation capability. Thus, the linear surface concavity in accordance with this invention retains the capability to form organized vortices for flow and heat transfer enhancement with low pressure penalty, but does so with a maximum of surface coverage by the enhancement over the entire linear xe2x80x9cfrontxe2x80x9d of the concavity. This arrangement can be used in virtually in any application in which fins, turbulators or the like are currently used for thermal enhancement, such as cooling passages of turbine blades, cold and/or hot side surfaces of components such as combustor liners, transition pieces, etc. and/or cooling channels in such components. This feature lends itself especially to cases where only a single xe2x80x9crowxe2x80x9d of concavities can be fitted, but is equally suitable for multiple linear concavity arrangements.
Accordingly, in one aspect, the present invention relates to a machine component having a surface provided with a heat transfer enhancement feature formed therein comprising at least one linear surface concavity comprised of plural overlapped concavities.
In another aspect, the invention relates to a turbine component having a cooling channel in a wall of the component, the cooling channel defined in part by two opposed walls, at least one of the walls having a heat transfer enhancement feature formed therein that includes at least one linear surface concavity comprising a plurality of overlapped concavities.
The invention will now be described in conjunction with the following figures.